Machining of materials to create openings or recesses of different shapes is used in the manufacture and repair of a wide range of objects. In applications where the dimensional tolerances, roundness and smoothness of the machined surface are important, special tools are often required, especially when the material to be machined is very hard or otherwise difficult to machine. For example, transfer machines within an automated manufacturing line often require multiple machining heads with a variety of different cutting bits to form rounded openings of the desired profiles. The more different machining heads required in a transfer machine, the more complex the machine becomes, and the more floor space it requires. As an alternative to multiple machining heads, a single cutting machine can be adapted to receive a variety of different cutting bits. However, when the cutting bit needs to be changed, the processing line must be paused or shut down, resulting in reduced throughput.
In an exemplary application, such cutting tools are used in the repair of the cylinders heads of internal combustion engines to re-establish the high quality seal required for efficient engine performance and fuel consumption. It is well known among vehicle mechanics that valve seats can be machined to remove the outer surface of the seat to expose a smooth and uniform contact surface by a technique commonly referred to as xe2x80x9clappingxe2x80x9d. This lapping technique is accomplished by removing the cylinder head from the engine and machining the valve seats with a cutting blade. Typically, a valve seat has a profile with three different angles: a throat angle, a valve seat angle, and a top angle. In order to simultaneously cut the different angles, a xe2x80x9cthree-anglexe2x80x9d cutting blade or bit is used. Each cutting edge of the three-angle cutting bit corresponds to one of the valve seat angles to be machined. Three-angle cutting bits vary in size and shape depending on the type of cylinder head valve seat being machined. These three-angle cutting bits are currently used by valve seat and guide manufacturers.
A disadvantage of the lapping technique is the risk of damage to the surface finish from vibration, chattering, or undulation generated by flexion of the cutting bits. This problem develops because certain cylinder head valve seat shapes require a three-angle cutting bit with a long cutting edge. Rotation of this long cutting edge when the edge is in contact with the work surface can create flexions in the cutting bit, especially when the material is difficult to machine, i.e., a very hard material. These flexions generate vibrations, chattering, or undulations which can disrupt contact between the cutting edge and the surface being cut. The skipping blade can damage the surface finish of the valve seat resulting in a machined valve seat that is not acceptable by Original Equipment Manufacturer (OEM) standards.
Another disadvantage of the lapping technique is a decentering phenomena. As stated above, cutting efforts with a long cutting edge/surface create flexions. These flexions create an unbalanced radial cutting effort which decenters the three-angle cutting blade, also resulting in unacceptable quality.
Still another disadvantage of the lapping technique is the large number of three-angle cutting blades needed to machine different types of valve seats. Each type of engine has a different valve seat profile. Thus, one or more unique three-angle cutting blades may be needed for each type of engine.
In view of the aforementioned inadequacies of the prior art, the need exists for a cutting tool and a method for machining rounded openings that produces a good quality finish and uses a universal cutting blade.
It is an advantage of the present invention to provide a universal cutting bit and bit holder having the ability to rapidly and precisely machine a wide range of openings or recesses of varied shapes and/or profiles.
It is also an advantage of the present invention to substantially reduce flexion of the cutting bit during machining.
It is another advantage of the present invention to eliminate decentering phenomena due to unbalanced radial efforts from flexion, and to eliminate concentricity defects resulting from cutting/machining effort.
Yet another advantage of the present invention is to eliminate vibrations, chattering, and undulations to provide improved finish for the machined surface.
Still another advantage of the present invention is to provide concentric machining for multiple contours within a opening.
In an exemplary embodiment, the present invention is a machining head of a machining apparatus comprising a spindle, a carriage head, a carriage head holder, a carriage feed driving assembly, and a universal cutting blade. A fixed pilot is attached to the bottom of the carriage head along the z-axis of a machine spindle to provide a means for centering the machining head in the opening to be machined, e.g., a valve guide of a cylinder head. The carriage head holder attaches to an extension of the machine spindle so that when the machine spindle is rotated, the machining head rotates. The carriage head is attached to the carriage head holder at an inclined angle relative to the bottom surface of the carriage head. The carriage feed driving assembly provides control of the inward and outward movement of the carriage head. The universal cutting blade is mounted on the carriage head through one of a plurality of mounting holes. For applications to cylinder head repair, the machining head can be utilized with virtually any conventional valve seat machining system, but is preferably used with the systems disclosed in U.S. Pat. Nos. 5,613,809, 5725,335, and 5,829,928 of Harmand, et al. (hereinafter the ""809, ""335, and ""928 patents, respectively) which are incorporated herein by reference.
The machining apparatus of the exemplary embodiment comprises a driving system, a machining head as described above, a pilot, a depth gauge, and a system controller. The driving system further comprises a machining sphere, a machine spindle, a spindle sheath, a rotational drive motor, and a vertical displacement motor. The spindle sheath is disposed within and supported by the machine sphere. The spindle sheath is fixed within the x-and y-axis, but can move along the z-axis by the vertical displacement motor. The vertical displacement motor is electrically connected and controlled by the system controller. The machine spindle is disposed within the spindle sheath and rotates around its z-axis through a drive motor. The drive motor rotating the machine spindle is electrically connected to and controlled by the system controller. The depth gauge is disposed on the spindle sheath by a fixed arm and is electrically connected to the system controller. The depth gauge measures the distance between a top surface of a cylinder head and the cutting blade. In a preferred embodiment, a second vertical displacement motor is provided so that feed of the arbor, which controls the carriage feed rate, is independent of the spindle feed which vertically moves the spindle, housing and all components therein relative to the working surface, providing three independent degrees of motion.
The system controller includes a memory which contains software for controlling the operation of the cutting tool. This system controller includes a user interface at which an operator can input the parameters that define the geometry of a valve seat profile. These parameters are used by the system controller to determine the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, the inward/outward displacement of the carriage head, and the number of rotations needed to machine a segment of the valve seat profile. The system controller uses a look-up table, stored externally or within internal memory, and the input information is used to determine the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, and the number of rotations needed to machine a segment of the valve seat profile. An operator simply centers the spindle, activates the system after the initial input of information for a given cylinder head and valve seat profile, and re-centers on each subsequent valve seat before activation.
For applications to transfer machines or other machining applications, the system controller coordinates operation of the machining head with the transfer of work pieces into a work station associated with the machining head. As with the embodiment for use for valve seat machining, the controller stores data including the parameters used to control the machining head to achieve the desired characteristics (profile, diameter, depth, finish smoothness, etc.) of the opening.